Device for continuous movement of objects with symmetry, use for visual inspection and control

ABSTRACT

This invention relates to a device for controlling a continuous movement of an object with symmetry of revolution ( 1 ) comprising a conveyor ( 5 ), characterized in that the conveyor comprises two parallel guides ( 6 ) and at least one pair of belts ( 8 ) stretched on the guides, between and on which these objects move at the level of the guides, these belts forming an angle ( 11 ) between a top track and a lower track of each of the belts, the belts in the pair having the same direction of rotation around the guides, the same value of the measured angle ( 11 ) from the upper track to the lower track, and the same displacement speed. Preferably, the pair of belts consists of a single folded belt.

[0001] The purpose of the invention is a device for continuous movementof objects with symmetry of revolution. One of the target applicationsis the inspection of cylindrical objects at a high speed.

[0002] Putting into movement in this case means a combined translationand rotation movement; objects rotate at the same time as they moveforwards, for example to present their entire lateral surface (forexample cylindrical) to sensors that will check their appearance orcharacteristics. It is desirable to have a device enabling a large flowof objects on a production or inspection line, by minimizingmanipulations of these objects that can follow each other, very closetogether, in a continuous flow. Therefore, the required movement typemust enable continuity of the production flow and displacement of eachobject at the same time. The device that satisfies this problem mustguarantee uniformity of movement—which must be perfectly continuous bothin translation along the main axis of the object, and in rotation aboutthis axis—for example to enable a good quality inspection (good qualityimages obtained in the visual and inspection application), even at highrate, despite constraints imposed on the advance speed of the objects.The design of this type of device must be based on a simple principle,and its operation must be easy to adjust.

[0003] Conveyor belts and other conveyance devices are well known, butthe need to rotate the objects at the same time as they are beingtranslated after orienting them correctly causes special problems. Theproduction of a system rotating and translating objects at the same timeis not easy since if two different forces are to be applied to theobject, the rotation and translation movements oppose each other whichcauses friction that reduces the smoothness of the final movement.However, there is a solution available in “centerless” grinding machinetools, that applies a rotation movement to cylindrical parts by skewapplied friction. In this case, the parts also move longitudinally. Butthis is only possible if the parts are sufficiently long. Furthermore,there is no guarantee of the flow continuity.

[0004] This principle is repeated in some inspection systems like thatpatented by the Rohrer Inc Company (US) in U.S. Pat. No. 5,249,912“Inspection apparatus” published on May 10, 1993. The double movement isthen applied to the cylindrical object by means of a belt that entrainsobjects in rotation by friction and a double guide above and throughthis belt that applies a translation movement to these objects. Theapplication divulged in this patent was an eddy currents inspection. Thesolution divulged in this patent consists of orienting the cylindricalobjects by making them slide under an inverted channel pathway thataligns their axes with the direction of advance, and rotation isachieved by passing the objects on an endless belt that moves in alateral direction (but not perpendicular) and forces a rolling movementon them.

[0005] Unfortunately, this system comprises limitations due to frictionbetween objects and the guide. This friction prevents a perfectlyregular helical movement at a high rate. The simultaneousrotation/translation movement imposed by the endless belt on an objectthat is stopped by a guide, regardless of the type of guide, necessarilygenerates friction between the object and the guide (inverted channel inthe patent mentioned above) that disturbs the uniformity of thismovement and cause jerks and vibrations on the object, particularly athigh speeds. This friction and its disturbing consequences can then blurthe images of the object taken with an optical detector, for example ina visual inspection. In this case, and particularly at high speeds, thisdevice cannot produce the very high quality images necessary for a highperformance inspection. Furthermore, if severely damaged parts appear,they may be entrained very irregularly, and the rotation movement wouldbe hindered or even actually stopped. The part is then very badlyentrained since apart from the fact that parasite friction affects themovement of the guide, there is only a single line of contact betweenthe part and the belt. Finally, the space available to containinspection sensors is reduced due to the presence of the guide (forexample a simple or double rail) and may be insufficient for inspectionapplications using sensors other than those described in the Rohrerpatent.

[0006] The device according to the invention is intended to improve themovement, and particularly to completely solve these disturbing frictionproblems by eliminating defects inherent to prior devices.

PRESENTATION OF THE INVENTION

[0007] This invention proposes a device to apply continuous movement toobjects with symmetry of revolution comprising a conveyor, characterizedin that the conveyor comprises two parallel guides (such as cylinders orrounded sabres) and at least one pair of belts pulled tight on each ofthe guides, between and on which the objects are moving at the samelevel as the guides, these belts forming an angle (11) between an uppertrack and a lower track of each of the belts, the belts in the pairhaving the same direction of rotation around the guides, the same valueof the measured angle (11) of the upper track to the lower track, andthe same displacement speed.

[0008] To simplify the presentation, the two parallel guides covered byportions of the moving belts will be called “guide-belts” in theremainder of this presentation, to express the fact that the objects arein contact with the moving portions of the belts covering the guides butare never in direct contact with the guides themselves. Each guide-beltforms an angle α (not a right angle) with the portion of the belt thatit guides; this angle depends directly on the angle 11.

[0009] The spacing between these two guide-belts is adjustable and isused to form a natural V-shape to guide objects that are entrained onboth sides by the belt system both in rotation and in translation, alongthe axis of this natural guide. The translation/rotation ratio dependson the angle (11) and may be adjusted by a variable orientation of thebelt with respect to its guide.

[0010] In this solution, there is no longer any parasite frictionbetween the part to be entrained/inspected and an artificial guide whichstops it, hindering the simultaneous rotation and translation movementdue to its inherent principle. Objects are then moved uniformly, and theinspection may take place even at high rate without any jerks orvibrations. Very high quality images are obtained if a visual inspectionis made.

[0011] The device according to the invention improves the entrainment ofobjects not only by elimination of jerks or vibrations, but also by alarger contact area, better distributed into several homokinetic areas(at least two edges of the object instead of a single contact line),between the object and the entrainment surfaces which improves theuniformity of the helical movement, even for damaged parts. Sinceobjects are directed by the spacing between the parallel guide belts,this adjustable spacing will be chosen to optimize entrainment/guidanceof objects as a function of their diameter. This spacing is chosen to belarger when the objects are larger, in order to give a better routing ofthe objects that will be supported more deeply in the V-shaped guidenaturally formed by the two portions of the belt, and also a betterentrainment by portions of belts that will have a better grip on theobjects with a greater spacing.

[0012] Finally, the space available to contain arbitrary sensors orother useful devices is completely free around the objects, over morethan 180 degrees around their lateral surface, since the presence of anartificial guide for the objects has completely disappeared.

[0013] According to a preferred embodiment of this movement deviceaccording to the invention, the belts in the pair belong to the samecontinuous loop, the lower tracks and the upper tracks being anextension of each other, the two connection tracks connecting the lowertracks and the upper tracks respectively. By this use of a singlerolling belt, displacement speeds at the guide-belts are simply andreliably synchronized.

[0014] This type of inspection device is applied to optical inspectionof objects by adding a light source to illuminate the object along atleast one generating line, an image sensor covering the field of thegenerating line and possibly a sensor, for example an optical sensorthat signals to the camera that an object has just been positioned inits field. This optional sensor is located on the path of the objectstransverse to their displacement.

[0015] This application to optical inspection makes use of a generalcharacteristic of the invention, which is the available space freedaround the objects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The preferred embodiment of the invention, that is not unique,will now be described with reference to the following figures:

[0017]FIG. 1 is an overview of the conveyor device from the top,

[0018]FIG. 2 is a side view of a new part of the conveyor device,

[0019]FIG. 3 illustrates an optical detector device.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0020] Refer to FIG. 1. The objects to be moved forwards so that theycan be examined may be cylindrical nuclear fuel pellets 1 originatingfrom an arbitrary feed device (for example firstly poured into avibrating bowl 2 and then passing along a chute 3 to fall onto aninclined gutter in which they are aligned); they arrive on the portionof the conveyor 5 associated with the optical detector (shown elsewhere)and that is specific to the invention.

[0021] The conveyor portion 5 comprises a pair of parallel guides 6 andan endless loop 7 stretched along a complex shape. It can be virtuallybroken down into a pair of belts 8 wound and stretched aroundguide-belts 6, that comprise an upper track 9 and a lower track 10adjacent to each other on and under the guides 6. The lower track 10 andthe upper track 9 are not exactly superposed but form an angle 11between them which is the same value (in quantity and in sign) for thetwo belts 8, when measuring from the upper track 9 to the lower track 10turning around a vertical axis. Furthermore, the upper tracks 9 have thesame orientation and the directions of rotation of the belts 8 aroundtheir corresponding guide 6 are the same, as is clearly shown in FIG. 2.The different guide-belts have exactly the same speed without the needfor a synchronization device since in this embodiment they physicallyform part of the same belt. The guide-belts 6 may be round bars orrounded solids such as sabres, in other words flat supports with an edgecurved along a semi-circle.

[0022] The result of this is that a pellet 1 arriving on and between thetwo belts 8 is subjected to a joint rotation and perfectly smoothtranslation movement since the two upper tracks 9 move it in the samemanner with the same rotation and translation speed along the guides 6.Therefore, without stopping, the pellet 1 moves successively along theportions of its side face with one detector which examines it duringthis time. The ratio of the rotation and movement speeds is adjusted bythe value of the angle 11. A pair of rolls 12 is used for each belt 8,in order to stretch the upper track 9 and the lower track 10 around therolls. In this embodiment, in which the belts 8 belong to a continuousloop 7, a single motor 19 driving one of the four rolls 12 is sufficientto apply the movement of the loop 7 which also includes two connectiontracks 13 and 14 stretched between the pairs of rolls 12 and whichconnect the upper tracks 9 and the lower tracks 10 respectivelytogether. The uniqueness of the loop 7 enables perfect synchronizationof the speeds of the belts 8. The rolls 12 can be installed on supportswith adjustable positions on a frame (not shown) to adjust the value ofthe angle 11 and the tension of the belts 8. Similarly, the spacingbetween the two parallel guide-belts 6 is adjustable, so that pelletscan be driven/guided as well as possible as a function of theirdiameter. When they have gone beyond the loop 7, the pellets 1 areretracted and drop into an opening 20 formed between the guides 6. Theyare then retrieved by an arbitrary evacuation device not shown. Note inpassing that the feed device, which may be arbitrary, could to someextent be made directly by the upper portion 8 of the belt on theupstream side of the conveyor central part, provided that the pelletsare put down correctly on the belt.

[0023] The effective manufacture of a visual inspection machine usingthe solution consisting of the single belt with double pass providing atwofold drive of cylindrical shaped nuclear fuel pellets is a means ofenabling a high inspection rate without any particular manipulation ofthe pellets, with very high quality images. The principle used hassimplified the design of this machine and its adjustment procedures.

[0024] In the preferred application in which the positioning device isapplied to a visual inspection, the detection device comprises a lightsource 15 directed towards the pellet 1 and that can emit a beam,preferably a plane beam, that illuminates a generating line on thepellet. The detector 16 consists of a linear strip of brightness sensors17 connected to a camera 18. The beam of the source 15 striking thegenerating line 25 of the pellet 1 is returned to the detector 16 inorder to form an image of this generating line, and the camera 18compiles images of generating lines as the pellet 1 moves forwards togive a global image of it. A sensor placed in front of the path of thepellets 1 may be used to detect arrival of the pellets in the field ofthe detector 16 and the camera 18 and begin taking photos. These imageacquisition processes are known and therefore no particular descriptionwill be given for them.

[0025] Defects of pellets 1 usually consist of dimensional errors orlocal surface defects such as splinters, cracks, open cavities, marks,scratches, pitting or inclusions of foreign bodies. In all cases, theyproduce a non-uniformity at the surface of the pellet 1. Lightoriginating from the source 15 is directed so that it is reflected tothe detector 16 when it reaches a generating line normal to the pellet1. Otherwise, the light is returned irregularly, very much weakened, oris not close to the sensors strip 17.

[0026] There are two possible variants that affect the method used toilluminate the object.

[0027] According to a first variant, the light may be grazing lightdirected to the upper generating line of the pellet 1, as shown in FIG.2. Under normal conditions, light is returned to the sensor strip 17 bydiffusion. If there is a cavity or a crack, etc., in pellet 1, lightwill not be intercepted and scattered again at this location, and thecorresponding sensors 17 are not illuminated. This method gives verygood results but requires a powerful source (or a very sensitivecamera/objective assembly) since the scattered light returned by thepellet is fairly weak. Furthermore, it must be possible to make a fineadjustment to the grazing position of the light beam.

[0028] According to a second variant, light may be directed towards anarbitrary generating line of the pellet 1 and returned by reflection.Light is reflected on a regular portion of the pellet with a maximumintensity exactly along the centreline of a well-positioned sensor, butconversely a surface defect no longer reflects the light beam along theaxis of this sensor and the fault will be seen as being much darker. Theadvantage of this method is that it requires much less powerfullighting; furthermore, the system is easy to adjust by adjusting theposition of the camera to produce a practically saturated image when theobjective is fully open.

[0029] The camera (16) is synchronized on the pellets by using anoptical micro-sensor operating in emission/reception, transverse to itsdisplacement. This type of sensor is fairly well known and is not shown.

[0030] This type of device can be used for many other applications inaddition to a visual inspection, such as an inspection using any othertype of sensor (optical, magnetic, electrical, ultrasound, eddy current,etc.).

[0031] The system may also be applied to any process other thaninspection that does not apply a large force to the object of revolutionto be treated.

[0032] More generally, the device enables entrainment of arbitrarilyshaped objects whenever they have symmetry of revolution (such ascylindrical, spherical objects, etc.).

1. Device for controlling continuous movement of objects with symmetryof revolution (1) comprising a conveyor (5), characterized in that theconveyor comprises two parallel guides (6) and at least one pair ofbelts (8) stretched over the guides, between and on which these objectstravel at the same level as the guides, these belts forming an angle(11) between an upper track and a lower track of each of the belts, thebelts in the pair having the same direction of rotation about theguides, the same value of the measured angle (11) from the upper trackto the lower track, and the same displacement speed.
 2. Device forcontrolling continuous movement according to claim 1, characterized inthat the belts in the pair form part of the same continuous loop (7),the lower tracks (10) and the upper tracks (9) being continuous witheach other, the two connection tracks (13, 14) connecting the lowertracks and the upper tracks respectively.
 3. Device for controllingcontinuous movement according to either of claims 1 or 2, characterizedin that it is used with a detector (16) consisting of a sensor or a rowof sensors (17) parallel to the guides (6) and sensitive to a lightreflected or scattered by the objects (1).
 4. Device for controllingcontinuous movement according to claim 3, characterized in that thelight is grazing, aimed at the upper generating line of the object andreflected by diffusion to the strip of sensors
 17. 5. Device forcontrolling continuous movement according to claim 3, characterized inthat the light is directed towards any generating line of the object 1and reflected to the strip of sensors (17).
 6. Device for controllingcontinuous movement according to any one of claims 1 and 2,characterized in that it comprises a sensor on the path of the objects(1) that is capable of signalling to the camera that an object has justbeen positioned in its field.
 7. Device for controlling continuousmovement according to any one of claims 1 to 6, characterized in that itis associated with a system (16) for detection of defects in objects(1).
 8. Application of the device for controlling continuous movementaccording to any one of claims 1 to 6, to the optical inspection ofnuclear fuel pellets.